Various technologies use membranes, including those membranes that apply reverse osmosis. A disadvantage in the use of membranes is that during operation, the membranes gradually become fouled. In particular, biofilm growth and mineral deposits on membranes, including reverse osmosis membranes, nanofiltration membranes, ultrafiltration membranes, and microfiltration membranes, can have detrimental results. Such biofilm growth and mineral deposits can cause severe flux declines, increased pressure, reduced production, can negatively impact the quality of finished goods, and often results in premature replacement of such membranes.
Membranes provided within a separation facility can be treated using clean-in-place (CIP) methods to provide flushing, rinsing, pretreatment, cleaning, and preserving, as filtration membranes have a tendency to foul during processing. Fouling manifests itself as a decline in flux and an increase in pressures with time of operation leading to decreased production. Flux decline is typically a reduction in permeation flow or permeation rates that occurs when all operating parameters, such as pressure, feed flow rate, temperature, and feed concentration are kept constant. In general, membrane fouling is a complicated process and is believed to occur due to a number of factors including electrostatic attraction, hydrophobic and hydrophilic interactions, the deposition and accumulation of feed components, e.g., suspended particulates, impermeable dissolved solutes, and even normally permeable solutes, on the membrane surface and/or within the pores of the membrane. It is expected that almost all feed components will foul membranes to a certain extent. See Munir Cheryan, Ultrafiltration and Microfiltration Handbook, Technical Publication, Lancaster, Pa., 1998 (Pages 237-288). Fouling components and deposits can include inorganic salts, particulates, microbials and organics.
Filtration membranes typically require periodic cleaning to allow for successful industrial application within separation facilities such as those found in the food, dairy, beverage and energy industries. The filtration membranes can be cleaned by removing foreign material from the surface and body of the membrane and associated equipment. The cleaning procedure for filtration membranes can involve a clean-in-place CIP process or in situ cleaning where cleaning agents are circulated over and through the membrane to wet, soak, penetrate, dissolve and/or rinse away foreign materials from the membrane. Various parameters that can be manipulated for cleaning typically include time, temperature, mechanical energy, chemical composition, chemical concentration, soil type, water type, hydraulic design, and membrane materials of construction.
Conventional cleaning techniques include the use of high heat and/or extreme pH, i.e., very high alkalinity use solutions, or very low pH acidic use solutions. However, many surfaces cannot tolerate such conditions. For example, membranes used in the energy services industry often have specific limitations with respect to the temperature and pH at which they can be operated and cleaned due to the material from which they are constructed.
In general, the frequency of cleaning and type of chemical treatment performed on the membrane has been found to affect the operating life of a membrane. It is believed that the operating life of a membrane can be decreased as a result of chemical degradation of the membrane over time. Various membranes are provided having temperature, pH, and chemical restrictions to minimize degradation of the membrane material. For example, many polyamide reverse osmosis membranes have chlorine restrictions because chlorine can have a tendency to halogenate and damage the membrane. Cleaning and sanitizing filtration membranes is desirable in order to comply with laws and regulations that may require cleaning in certain applications (e.g., oil and gas production), reduce microorganisms to prevent contamination of the product streams, and optimize the process by restoring flux (and pressure).
Both oxidizing and non-oxidizing biocides are conventionally used in combination with alkaline treatments for disinfection of a membrane and to prevent or reduce the fouling of the membrane. Exemplary oxidizing agents are chloric compounds, which are known to have strong anti-microbial effects, however they have a significant disadvantage in that they may damage the membrane surface. Such contact with membrane surfaces is a required part of the disinfectant process using the oxidizing biocide. Other exemplary techniques for cleaning membranes are disclosed by U.S. Pat. No. 4,740,308 to Fremont et al.; U.S. Pat. No. 6,387,189 to Groschl et al.; and U.S. Pat. No. 6,071,356 to Olsen; and U.S. Publication No. 2009/0200234.
Various methods of cleaning membranes are known to decrease the lifespan of a membrane as a result of damaging the membranes and surrounding equipment that is to be cleaned. For example, an acid treatment might have a corrosive effect on the surfaces of process equipment and on filtration membranes used therein. Also, the rather high temperature required entails an increase in energy costs. Furthermore, the use of large volumes of acidic inactivation compositions requires their neutralization and proper disposal of the liquid waste. These and other known disadvantages of membrane cleaning systems are known.
In the context of energy services, there are additional concerns regarding water sources and the compatibility of these with the peroxyformic acid compositions of the invention for cleaning membranes. In an aspect, in the context of offshore oil and gas facilities there are concerns regarding the water sources available, namely sea water, brine water, brackish water and produced water. The additional presence of ions such as chloride, divalent metals and sulfate can further damage the membrane and present issues in terms of compatibility of treatment and cleaning protocols with the membrane material. Further, the complex diversity of the species of microbes present in these waters can lead to an increase in biological fouling and the accumulation of biofilm on membrane surfaces. These are exemplary concerns uniquely present in the treatment of membranes for energy services applications. These concerns illustrate the need for membranes to separate out many species in sea water and other conditions used in oil and gas platforms. In particular, it is a need to use membranes to separate out sulfate from seawater in an oil and gas open sea platform.
Although various agents preventing microbial growth, such as oxidizers, have been used for membrane cleaning there is still a need for an improved method for the prevention of microbial growth and biofilm formation on membranes.
Accordingly, it is an objective of the claimed invention to provide peroxyformic acid compositions generated in situ for the prevention of mineral scale formation, deposit build up and removal of microbial growth on membranes and biofouling of membranes. In particular, it is an object of the invention to provide a method, which does not damage the membranes and which mitigates microbial growth and biofouling on the membranes.
A further object of the invention is to replace 2,2-dibromo-3-nitrilopropionamide (DBNPA), a traditional biocide that hydrolyzes under both acidic and alkaline conditions, with the peroxyformic acid compositions according to the invention.
A further object of the invention is to provide a membrane-compatible composition, such that the composition does not contain any components destroying or blocking the membrane, and/or generate chlorine species causing damage to membranes.
Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawings.